This invention relates generally to broadband communications systems, such as hybrid/fiber coaxial (HFC) systems, and more specifically to an ingress monitoring device that is used in the broadband communications system.
FIG. 1 is a block diagram illustrating an example of one branch of a conventional broadband communications system, such as a two-way hybrid/fiber coaxial (HFC) system, that carries optical and electrical signals. Such a system may be used in, for example, a cable television network; a voice delivery network, such as a telephone system; and a data delivery network to name but a few. The communications system 100 includes headend equipment 105 for generating forward signals (e.g., voice, video, or data signals) that are typically transmitted as optical signals in the forward, or downstream, direction along a first communication medium 110, for example, transmitting such signals at a 1550 nano meter (nm) wavelength over fiber optic cable. Coupled to the headend equipment 105 are hubs 115 that include equipment that further transmits the optical signals over a second communication medium 120. The second communication medium 120 may transmit, for example, 1310 nm signals over fiber optic cable.
The signals are then transmitted to an optical node 125 that converts the optical signals to radio frequency (RF), or electrical, signals. The electrical signals are further transmitted along a third communication medium 130, such as coaxial cable, and are amplified and split, as necessary, by one or more distribution amplifiers 135a-c positioned along the communication medium 130. Taps 140 then further split the forward signals for provision to subscriber equipment 145, such as set-top terminals, computers, telephone handsets, modems, and televisions. It will be appreciated that only one branch connecting the headend equipment 105 with the plurality of subscriber equipment 145 is shown for simplicity; however, there are typically several different branches connecting the headend equipment 105 with several additional hubs 115, optical nodes 125, amplifiers 135a-c, and subscriber equipment 145.
In a two-way system, the subscriber equipment 145 can also generate reverse signals that are transmitted upstream through the reverse path to the headend equipment 105. Such reverse signals may be combined via the taps 140 and passive electrical combiners (not shown) with other reverse signals and then amplified by any one or more of the distribution amplifiers 135a-c. The electrical signals are typically converted to optical signals by the optical node 125 before being provided to the headend equipment 105. It will be appreciated that in the electrical, or coaxial cable, portion of the network 100, the forward and reverse path signals are carried along the same coaxial cable 130. In contrast, the reverse optical signals are typically carried along a different reverse fiber (not shown) than the forward fiber 120, 110 carrying forward optical signals.
In addition to reverse signals emanating from subscriber equipment 145, unwanted ingress, or excess noise, may also be transmitted along the reverse path that affects the quality of the reverse signals. The more complex and efficient the modulation scheme, such as quadrature amplitude modulation (QAM) signals, the more ingress will affect the quality of received signals. A large portion of the reverse ingress enters the system through, for example, defective connectors and poorly shielded cable and components located in the coaxial portion of the network 100. As a result, a great deal of effort has been devoted to understanding and quantifying ingress. Studies have shown that the majority of ingress originates at or around the subscriber""s premise. For example, electric motors, radio transmitters, CB radios, and automobile ignitions when activated may cause ingress at a faulty point in the cable or connectors. Unfortunately, however, ingress varies substantially from system to system, from hour to hour, and from day to day. It will be appreciated that though noise signals travel along both the forward and reverse paths, ingress signals affect the reverse path.
To mitigate the effects of ingress on the quality of signals received at the headend, operators can improve the quality of connectors and cable used during the initial installation of the system. They can also ensure that the connectors are properly fitted and sufficiently tight. Moreover, the operator can allocate reverse signals to higher frequencies within the reverse band. For example, a typical reverse band may be from 5 Mega Hertz (MHz) to 42 MHz. An operator may then allocate high-speed, complex signals that carry high-priority signals, such as impulse pay-per-view or cable modem signals, to the higher frequencies within the reverse band. In comparison, low-speed, rugged signals that carry low-priority or repetitive traffic, such as system management signals, can be transmitted in the lower more easily susceptible frequencies in the reverse band.
Conventionally, ingress troubleshooting is difficult and cumbersome, and typically only begins when a subscriber calls in with a service problem that they may be experiencing. A headend technician and field technicians then have to work cooperatively to locate the point of ingress. A headend technician may, for example, connect a spectrum analyzer to receiver equipment and analyze the power spectrum of each frequency within the band (i.e., from 5 MHz to 42 MHz) as the field technicians disconnect the reverse path in various locations along the affected branch until the ingress is located. More specifically, ingress is displayed on a spectrum analyzer as unwanted signals between the expected noise floor and the signals within the expected frequency for each particular channel. When the field technician disconnects the reverse path in certain areas, the headend technician monitors the spectrum analyzer for the disappearance or appearance of the ingress. One of the major difficulties in locating the point of ingress, however, is that ingress is fleeting; it is not a constant that can easily be viewed at all times. Therefore, the ingress may not be present when the technicians are trying to locate the faulty point. Another inconvenience is that the reverse path is disconnected for the period of time it takes to consult the spectrum analyzer for each frequency level. Consequently, locating the point and cause of ingress takes a tremendous amount of time, money, and dissatisfied subscribers along the entire reverse path branch.
Therefore, what is needed is a device and a system that is able to quickly determine the general point of ingress without the need of several technicians in the field and, additionally, without having to wait for the customer""s service call. The device may also quantify the ingress and return statistical data that may be of use for the operator regarding the conditions in the system.